1. Technical Field
This invention relates generally to exhaust systems for internal combustion engines.
2. Description of Related Art
In the early days of exhaust development, when flat head engines were common, scavenge resonant exhaust systems helped to remove residual exhaust gases from the combustion chamber & helped to initiate intake flow into the combustion chamber. Scavenge has evolved into expanding tube extractors, anti-reversion mufflers and structures to prevent loss of scavenge vacuum at low rpms. During this time, cylinder head design has evolved from flat heads to overhead designs incorporating three, four, five and even eight valve per cylinder designs. Combining state of the art scavenge technology with state of the art head designs creates “overscavenge;” a situation where raw, unburned air fuel is swept through the combustion chamber during valve overlap, and out of the tail pipe. Horsepower is lost due to reduced dynamic cylinder pressure. Fuel economy is lost due to the quantity of fuel and free radicals left unburned. Emissions increase as unburned matter is vacuumed out of the engine into the atmosphere. Catalytic converters were added in 1975 to incinerate such unburned products; restricting flow while emitting cyanide (CN—) compounds.